The present invention relates in general to the routing and flow path for recirculating exhaust gas (EGR) and the routing and flow path for blow-by (crankcase vent) gas. More specifically the present invention relates to the use of a control valve in cooperation with a venturi design in the flow path to introduce exhaust gases into the intake manifold in a mix with fresh charge air from the turbocharger.
At the present time blow-by (crankcase vent) gas of medium and heavy duty diesel engines is typically vented to the atmosphere. However, it is expected that in the near future environmental/emissions legislation will mandate that this gas be recirculated into the fresh charge air. The expected legislation will likely be similar if not the same as what is now in effect for gasoline engines and light duty diesel engines.
In anticipation of such legislation, some thought must be given to where and how such blow-by gas can be integrated into the air/gas flow network. One option, routing the blow-by gas in front of the compressor of the turbocharger is not desirable due to fouling of the wheel and aftercooler by oily deposits and other particulate matter.
In one embodiment of the present invention a venturi, with a cooperating control valve, is placed in the flow path downstream of tile aftercooler so as to induce the flow of blow-by gas into the fresh charge air. The induced flow is created by having a low enough static pressure at the throat of the venturi. Several venturi designs are disclosed, each of which is suitable for the present invention. In a related embodiment of the present invention, the venturi/control valve combination is placed in the flow path downstream of the aftercooler so as to induce the flow of EGR into the fresh charge air.
One application proposed for EGR, as conceived by the present inventors, is to use EGR as a means of reducing NO.sub.x in medium and heavy duty turbocharged diesel engines. For such engines EGR should be introduced at various speed and load conditions to be effective in NO.sub.x reduction due to the type of transient testing required by EPA and CARB.
It is generally recognized that the production of noxious oxides of nitrogen (NO.sub.x) which pollute the atmosphere are undesireable and in many cases are controlled by limits established by local, state and federal governmental regulations. The presence of NO.sub.x in the exhaust of temperature causes an increase in the amount of NO.sub.x present internal combustion engines is determined by combustion temperature and pressure. An increase in combustion in the engine exhaust. It is therefore desireable to control the combustion temperature in order to limit the amount of NO.sub.x present in the exhaust of an internal combustion engine.
One possibility for limiting or controlling the combustion temperature is to recirculate a portion of the exhaust gas (EGR) back to the engine air intake. Since the exhaust gas has a higher specific heat, the combustion mixture will burn at a lower temperature. The lower combustion temperature will, in turn, reduce the amounts of NO.sub.x produced during combustion.
While NO.sub.x formation is known to decrease as the EGR flow increases, it is also known that this is accompanied by a deterioration of engine performance including, but limited to, an increase in engine roughness and a decrease of power output within increasing EGR. Therefore, one factor limiting the magnitude of EGR is the magnitude of EGR-induced performance deterioration or roughness that can be tolerated before vehicle driveability becomes unacceptable. Furthermore, EGR should not be turned on during load transience, as this causes "incomplete combustion" which results in black smoke from the engine exhaust. It is also usually desireable that EGR be turned off during hard acceleration so that the engine may operate at maximum power output.
Determining the proper amount of EGR under varying engine operating conditions is a complex task. Most prior art control systems utilize at least two sensed engine parameters as inputs to the control system which controls the EGR. For example, U.S. Pat. No. 4,224,912 issued to Tanaka utilizes both engine speed and the amount of intake air as control variables. U.S. Pat. No. 4,142,493 issued to Schira et al. utilizes either engine speed and manifold absolute pressure or engine speed and throttle position. U.S. Pat. No. 4,174,027 issued to Nakazumi utilizes both clutch-actuation detection and throttle valve-opening detection as input variables to the control system. These methods all require the monitoring of several engine parameters, which may have a significant cost impact if the monitored signals are readily available within the engine. It is, therefore, desirable to control the EGR with a single monitored engine parameter as input to the control system in order to reduce the complexity of the control system, thereby improving cost efficiency and system reliability.
EGR control systems need to be carefully reviewed because many designs cannot be used with diesel engines. Diesel engines differ from spark ignition engines in a number of important ways, one being that the diesel engine does not include a valved, or throttled, intake manifold into which the combustion air is induced through a throttle and valve. Accordingly, the vacuum pressure existing in a diesel engine intake duct is slight at most. The source of vacuum pressure provided by the intake manifold of a spark ignition engine is, therefore, not available in a diesel engine. Hence, any prior art control system utilizing the vacuum pressure as an input to the control system will not work with a diesel engine.
In a diesel engine, the engine speed under a given load is controlled by the quantity of fuel injected into tile engine combustion chambers and accordingly the "throttle" of the diesel engine is considered to be a manually operated foot pedal connected by a linkage to a fuel pump for supplying the engine fuel injectors. The foot operated pedal is actuated to govern the quantity of fuel delivered by the fuel pump to the combustion chambers of the engine and thus controls the engine speed under a given load. Since the quantity of fuel introduced into the combustion chamber varies, the production of NO.sub.x varies as a function of the throttle setting. This being the case, it is theoretically possible to control EGR in a diesel engine using only the throttle position as an input to tile control system.
The present invention is therefore directed toward providing an EGR control system which utilizes only throttle position as an input to the control system. Such a control system could then be used with a diesel engine.
In medium and heavy duty turbocharged diesel engines the intake manifold pressure (boost) is typically higher than exhaust pressure in front of the turbine of the turbocharger. Therefore, one choice would be to route the exhaust gas to the inlet of the compressor of the turbocharger. However, this is not a good practice due to the fouling of the compressor wheel and possibly the aftercooler due to particulate in tile exhaust gas. Also, the compressor wheel which is typically made of aluminum cannot tolerate the high temperature of the incoming mixture of fresh air and exhaust gas due to the very high temperature of the compressed mixture at the point of leaving the wheel.
In another related embodiment of the present invention a venturi, with a cooperating control valve, is placed in the fresh charge air flow line between the compressor and aftercooler and is connected to an exhaust gas flow line whose input side is connected between the exhaust manifold and the turbine. Static pressure at the throat of the venturi is sufficiently low so as to induce the flow of exhaust gas into the flow of fresh charge air.
With regard to the various embodiments of the present invention, the following list of U.S. patent references is believed to provide a representative sampling of the types of flow paths and flow arrangements which have been conceived of in order to deal with blow-by gas and recirculating exhaust gas.
______________________________________ U.S. Pat. No. Patentee Date Issued ______________________________________ 3,877,477 Bader Apr. 14, 1975 3,925,989 Pustelnik Dec. 16, 1975 4,034,028 Tsoi-Hei Ma July 5, 1977 4,206,606 Yamada Jun. 10, 1980 4,363,310 Thurston Dec. 14, 1982 4,462,379 Tsuge et al. Jul. 31, 1984 4,478,199 Narasaka et al. Oct. 23, 1984 4,479,478 Arnaud Oct. 30, 1984 4,501,234 Toki et al. Feb. 26, 1985 4,669,442 Nakamura et al. Jun. 2, 1987 4,773,379 Hashimoto et al. Sep. 27, 1988 4,924,668 Panten et al. May 15, 1990 5,061,406 Cheng Oct. 29, 1991 5,094,218 Everingham et al. Mar. 10, 1992 5,203,311 Hitomi et al. Apr. 20, 1993 ______________________________________
While each of the foregoing references describe certain flow paths and flow arrangements, none are believed to include all of the novel features of the present invention.